As is well known in the art, Ethernet is a widely used network technology and has proved its reliability and quality in extreme conditions. Ethernet's wide proliferation, high bandwidth, and simple protocol make it an excellent connectivity solution.
A problem with using Ethernet in an automobile however is the limited number of options available to manage the network power consumption. This results in the system requiring a high power consumption in some cases that is not feasible in automobiles. The standard and common techniques that could be used in the context of power management of Ethernet devices include Power over Ethernet (PoE) and Wake-up on LAN (WoL).
As is known in the art, a communications network comprises a plurality of nodes. In an Ethernet communications network, each node comprises one or more hosts (or network devices), on which an application runs, and an Ethernet transceiver. The Ethernet transceiver forms in an interface between the one or more network devices (or hosts), and the network itself, and is therefore known as a network interface. Within a node, it is also necessary to have an internal node interface to allow access to the network interface by the one or more network devices within a particular node. An example of an internal node interface is a processor bus.
Nodes forming a switched Ethernet communications network may be categorised as either end nodes, or as switches.
An end node comprises one or more network devices and a network interface. A switch interconnects end nodes and comprises one or more switch ports equipped with a network interface.
The Wake-up On LAN (WoL) technique makes it possible to wake-up a host. However, because the remote wake-up is based on the detection of a data pattern in the payload of the packet of the Ethernet PHY (physical layer) this layer of the network must be kept alive at all times to be able to decode bits. This activity represents a few hundreds of miliwatts. This is orders of magnitude too high for automotive markets.
Power over Ethernet (PoE) delivers power over standard Ethernet cables. PoE can be used to supply power to nodes through the Ethernet cables. When used in a vehicle, the voltage level must be adapted to match the automotive environment requirements. This means that the network nodes can be completely shut down, for example when the car is locked. However the technique does not allow a node or a group of nodes to wake-up under their own initiative as in any centralized power management system.
As is known in the art, switched Ethernet network topology is based on a star or multi-star format. FIG. 1 is a schematic illustration of a known switched Ethernet network topology. The network illustrated in FIG. 1 is installed in an automobile.
In order to reduce power consumption of the network infrastructure, it is desirable to be able to shut down any unused or infrequently used node in a network.
A network device such as an end node or a switch may be powered off when the particular device does not participate in the network. When a device is powered off, no information can be exchanged with that device. This means that not only can the network interface be shut down, but that the hardware of the application may also be shut down.
In the network shown in FIG. 1 only the rear seat units (RSU) are active and, it is possible to completely power off devices that are connected to the unused ports.
It is, however, necessary for at least one node in the network to remain active and to be connected to a central power management unit of the vehicle in order to be able to power off the entire system, for example, when the doors of the car are locked. In the system illustrated in FIG. 1 it is the seven port switch that is the node that remains at least partially active and is connected to the central power management unit.
Generally, a network interface will be shut down with/by the host to which it interfaces. In such a case the host is no longer reachable. Most systems work in this way because it is the host that requests access to the network rather than a network requesting access to the host.